metamorphic
Quartzite Pebble
Metamorphic Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: White to light grey, Luster: Vitreous to dull, Crystal structure: Trigonal (granular texture), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: White to light grey, Luster: Vitreous to dull, Crystal structure: Trigonal (granular texture), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz sandstone under high heat and pressure, typically during mountain-building events. The individual sand grains recrystallize into a locked mosaic of quartz crystals.
Uses & applications
Commonly used in road construction, as railroad ballast, and in architectural landscaping. Pure varieties are used to produce silica sand for glassmaking.
Geological facts
Quartzite is so durable that it often survives intense weathering better than the surrounding rocks, frequently forming the caps of hills and ridges.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Often found in riverbeds or beaches as smooth, water-worn pebbles.
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